Aerodynamic instabilities, such as but not limited to flutter, can occurs in a gas turbine engine when two or more adjacent blades of a rotor of the engine, such as the fan, vibrate at a frequency close to their natural frequency and the interaction between adjacent blades maintains and/or strengthens such vibration. Other types of aerodynamic instability, such as resonant response, may also occur and are undesirable. Prolonged operation of a rotor undergoing such aerodynamic instabilities can produce a potentially undesirable result caused by airfoil stress load levels exceeding threshold values. Attempts have been made to mechanically or structurally mistune adjacent blades of such rotors, so as to separate their natural frequencies. Such solutions however introduces a level of manufacturing complexity that is not always desirable. Aerodynamically mistuning adjacent blades so as to reduce flow induced resonance has been attempted, but existing solutions have however shown limits during certain irregular operating conditions, such as during cross-wind operating conditions which may result in sudden nacelle ingestion of flow vortices.
There is an ongoing need for mitigating aerodynamic instabilities.